Vacuum cleaners are usually supplied with a range of tools for use with various cleaning situations that a user may encounter. An upright vacuum cleaner has a wide, floor-engaging cleaner head at the base of the cleaner which is used for general floor cleaning. A range of smaller tools may also be supplied with the machine. These are usually attached to the end of a flexible hose of the cleaner. The tools often include a crevice tool for use in narrow, confined spaces, a stair tool and an upholstery tool with a brush head. A cylinder or canister vacuum cleaner has a wide floor tool which is attached to the end of a cleaning wand for general floor cleaning and a similar range of smaller tools for use in other cleaning situations.
For any vacuum cleaner, it is important to maintain a good flow rate of air into the floor tool and along the suction path of the cleaner to maintain good cleaning performance. This is particularly important with a cleaner that relies on cyclonic or centrifugal separation as the flow rate of dust-laden air within the cyclonic separating chamber is an important factor in determining the efficiency of the dust separation. It is known for tools to include one or more bleed air inlets. As shown in FIG. 1, the air inlet of a crevice tool 10 has a flat portion 12, a notched portion 14 and an opening 15. The notched portion 14 ensures that some air flows into the tool 10 even when the flat portion 12 is sealed against a surface.
FIG. 2 schematically shows a known type of cyclonic vacuum cleaner. The vacuum cleaner 100 incorporates a floor tool 10 which is attached directly to a hose 114. The hose 114 is directly connected to dust-separating apparatus 116. The dust-separating apparatus 116 is a cyclonic separating apparatus using one or more cyclonic separation stages. Downstream of the dust-separating apparatus 116 is a pre-motor filter 120, followed by a fan 122 which is driven by a motor 124. A further filter 126 is located after the motor 124. A bleed valve 118 is located on the dust-separating apparatus. The bleed valve 118 is arranged to admit air into the separating apparatus when the flow of air along the airflow path is significantly reduced. The bleed valve can respond to the pressure along the airflow path reducing to a predetermined absolute value, or to the difference in pressure between two parts of the airflow path reaching a predetermined value.
In use, the motor 124 operates to activate the fan 122 which causes a flow of air to pass from the floor tool 10 to the dust-separating apparatus 116 via the hose 114. After separation has taken place, the airflow passes through the pre-motor filter 120, past the fan 122, past the motor 124 providing a cooling effect, and through the post-motor filter 126 before being expelled to the atmosphere. A bleed valve 118 is arranged such that, if the pressure within the dust-separating apparatus 116, and particularly at the location within the dust-separating apparatus 116 at which the bleed valve 118 is placed, drops below a pre-determined value, the bleed valve 118 opens so as to allow air from the atmosphere to enter the cyclonic dust-separating apparatus in order to maintain an adequate airflow to effect separation. The prevention of the airflow from falling below a predetermined level helps to ensure that the motor 124 is adequately cooled so as to prevent any risk of overheating in the event of a blockage occurring in the airflow path upstream of the bleed valve 118.
However, the provision of a bleed valve, particularly a pressure differential bleed valve, adds considerable cost to the cleaner. Also, since the bleed valve has movable parts it is prone to wear and degradation over a period of use.